Efficient treatment of perfluorohexanoic acid by nanofiltration followed by electrochemical degradation of the NF concentrate

Abstract

The present study was aimed at the development of a strategy for removing and degrading perfluorohexanoic acid (PFHxA) from industrial process waters at concentrations in the range 60-200 mg L. The treatment train consisted of nanofiltration (NF) separation followed by electrochemical degradation of the NF concentrate. Using a laboratory-scale system and working in the total recirculation mode, the DowFilm NF270 membrane provided PFHxA rejections that varied in the range 96.6-99.4% as the operating pressure was increased from 2.5 to 20 bar. The NF operation in concentration mode enabled a volume reduction factor of 5 and increased the PFHxA concentration in the retentate to 870 mg L. Results showed that the increase in PFHxA concentration and the presence of calcium sulfate salts did not induce irreversible membrane fouling. The NF retentate was treated in a commercial undivided electrochemical cell provided with two parallel flow-by compartments separated by bipolar boron doped diamond (BDD) electrode, BDD counter anode, and counter cathode. Current densities ranging from 20 to 100 A m were examined. The electrochemical degradation rate of PFHxA reached 98% and was accompanied by its efficient mineralization, as the reduction of total organic carbon was higher than 95%. Energy consumption, which was 15.2 kWh m of treated NF concentrate, was minimized by selecting operation at 50 A m. While most of the previous research on the treatment of perfluoroalkyl substances (PFASs) focused on the removal of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), these compounds have been phased out by chemical manufacturers. Our findings are relevant for the treatment of PFHxA, which appears to be one of the present alternatives to long-chain PFASs thanks to its lower bioaccumulative potential than PFOA and PFOS. However, PFHxA also behaves as a persistent pollutant. Moreover, our results highlight the potential of combining membrane separation and electrochemical oxidation for the efficient treatment of PFAS-impacted waters.

Efficient removal of per- and polyfluoroalkyl substances (PFASs) in drinking water treatment: nanofiltration combined with active carbon or anion exchange

“…17 Therefore, treatment of the concentrate laden with PFASs and other contaminants remains a challenge and is considered one of the main limitations of membrane filtration. 12,[18][19][20] Few studies exist evaluating differences in PFAS adsorption of both GAC and AIX sorbents in a direct comparison. Even fewer studies exist combining full-scale membrane techniques with pilot-scale GAC and AIX filters, respectively, even though this treatment set-up is being discussed as having the potential to be a new standard approach for the removal of PFASs in full-scale drinking water treatment.…”

Efficient electrochemical degradation of poly- and perfluoroalkyl substances (PFASs) from the effluents of an industrial wastewater treatment plant

“…which is significantly reduced to 153 kWh/m 3 when the target PFASs removal rate is set at 98% (treatment time 6 h). Therefore, energy consumption, that is strongly dependent on the target PFASs removal rate [55], and the potential formation of disinfection byproduct could be considered the main drawbacks of the electrochemical treatment. In this way it is demonstrated that the electrochemical treatment of the industrial WWTP effluent with BDD anodes allows the effective removal of PFASs at the same time that the general TOC content is nearly completely eliminated.…”

Understanding and Managing the Potential By‐Products of PFAS Destruction

“…The alternative approaches are emerging as more mobile options using small‐scale plants, which could be applied at sites where PFAS waste concentrates are generated. Based on numerous sources, an approximate range of energy demand per volume treated for plasma, electrochemical treatment, and sonolysis is 0.01 to 0.5‐kW h per liter (kW‐h/L; 0.04 to 1.9 kW‐h per gallon [kW‐h/gal]; e.g., Gomez‐Ruiz et al ; Soriano et al ; Kempisty et al ; Nzeribe et al ; Singh et al , ). However, approximating a range of energy demand for these relevant technologies is difficult to accurately summarize due to the variety of operating conditions within the respective studies when the energy demand was determined.…”

“…, ), electrochemical treatment (Schaefer et al. ; Soriano et al ; Schaefer et al ; Pica et al. ; Schaefer et al ), and sonolysis (Vecitis et al ; Campbell et al.…”

“…The first (primary) is a direct electron transfer at the surface of the anode (Zhuo et al ). This makes the anode a design parameter, with many sources suggesting that boron‐doped diamond anodes are more advantageous than mixed metal oxide anodes due to their commercial availability, high reactivity, low adsorptivity, and ability to defluorinate a wide range of PFAS (Trautmann et al ; Schaefer et al ; Soriano et al ; Schaefer et al ; Schaefer et al ). This direct electron transfer from the PFAS molecule to the anode is theorized to be a sequential defluorination process that may generate short‐chain PFAAs (Gomez‐Ruiz et al ).…”